1. Field of the Invention
The present invention relates to a control device for a high-pressure fuel system in a direct-injection internal combustion engine.
2. Description of the Related Art
The direct-injection internal combustion engine includes a fuel control section that measures fuel pressure in a fuel rail and calculates injector valve opening time (injection pulse width) in accordance with the measured fuel pressure for the purpose of enabling an injector to inject a target amount of fuel. One of the problems with the direct-injection internal combustion engine is fuel pressure pulsation in the fuel rail. Fuel pressure pulsation occurs because fuel discharge from a high-pressure pump and fuel injection from the injector are intermittent. This fuel pressure pulsation may cause the injector's fuel injection amount to deviate from a target controlled variable, thereby incurring exhaust deterioration.
The other problems with the direct-injection internal combustion engine are, for instance, fuel leakage from a high-pressure system and defects in the injector and high-pressure pump. Fuel leakage and defects may reduce fuel control accuracy, thereby causing exhaust deterioration. Therefore, methods for estimating the fuel pressure from controlled variables of the injector and high-pressure pump are proposed as conventional technologies for solving the above problems. For example, a technology disclosed in JP-A-2000-234543 varies a control gain to cope with fuel pressure pulsation, whereas a technology disclosed in Japanese Patent No. 3587011 estimates the fuel pressure and compares it with the measured fuel pressure to detect a defect.